Systems have been developed for monitoring characteristics, such as tyre pressure, tyre (air) temperature and/or acceleration of the wheels of a vehicle, or the battery voltage of a battery in a wheel mounted device. A wheel mountable device comprising one or more appropriate sensor(s) is located at each wheel, typically inside the tyre, which measures the relevant characteristic(s) and transmits corresponding information to a remote central monitoring station. An example of such a system is a Tyre Pressure Monitoring System (TPMS), of which the wheel mountable units are commonly referred to as tyre pressure monitors or tyre Pressure Monitoring (TPM) sensors.
Modern tyre monitors are typically snap-in type devices and so include a valve portion based on a conventional (with small modifications) snap-in tyre valve. Snap-in tyre monitors eliminate the need for a nut to hold the tyre monitor in place in the rim of the wheel on which it is mounted during use, which is advantageous since it simplifies the installation of the tyre monitor.
However, snap-in tyre monitors suffer from a problem at high vehicle speeds: as the vehicle accelerates from rest to higher speeds, a force is exerted on the tyre valve which becomes significant (for example 2000 g at very high speeds). This force increases with tyre monitor mass and with the speed of the vehicle. The relatively high forces can cause damage to rubber portions of the valve to the extent that an air leak can be caused (clamp in type tyre monitors do not have rubber on the valve, they still experience the force but are less prone to leaks because the valve is fixed rigidly with the retaining nut).
It would be desirable to reduce the mass and preferably also size of tyre monitors, especially but not exclusively to mitigate the above-identified problem relating to snap-in tyre monitors.